In a variety of electrical systems such as, for example, ignition systems for gasoline engines, emergency lighting systems, marine power systems, portable television sets and radio receivers, storage batteries have been employed to retain and store electrical energy for subsequent use. In their most common applications, storage batteries, also known as electric accumulators or secondary batteries, have been utilized in motor vehicles to provide power for starting the engine and for operating accessory equipment such as lights, radios and the like. Storage batteries usually provided for this use are of the lead-acid type that include an assembly of voltaic cells connected in series and which operate by a reversible electrochemical action. In this manner, the battery can be recharged by passing a current through the cells in the opposite direction to that of discharge, and for that purpose an alternator is usually provided on the motor vehicle.
Because of the electrochemical action and certain structural deficiencies within storage batteries, problems frequently develop that prevent operation or impair performance of the battery. To test a battery's condition, a suitable indicator may be connected to the terminals and a determination made of the relative magnitude of the voltage capability of the battery. This test, however, will demonstrate only short circuits within the battery, or insufficient voltage capacity under a no-load condition; that is, when very little, if any, current is being drawn from the battery. This test is incapable of determining the charge capacity or the ability of the battery to provide an adequate and substantially stable voltage while discharging a large current over a period of time. Thus, merely measuring the voltage capability under no-load conditions is generally considered inadequate for testing a battery's operability.
In an attempt to more effectively test a battery's operability, it has previously been proposed to provide battery testing devices capable of testing a storage battery under load conditions. One example of such a testing device is disclosed in U.S. Pat. No. 1,907,682 to Taylor. However, the testing device of the Taylor patent is only capable of testing batteries under load conditions; i.e., it is incapable of testing batteries under both no-load and load conditions.
Testing devices capable of testing batteries under both no-load and load conditions have also been proposed heretofore, as disclosed, for example, in U.S. Pat. No. 1,882,581 to Haskins. However, testing devices of a type similar to that disclosed in the Haskins patent have provided no limitation upon either the duration of the test or the magnitude of current drawn from the battery during the test. As is well known in the battery testing art, if a test is conducted for too long a period, damage to the battery may result even if only normal current is drawn from the battery. Further, if abnormally high current is drawn from the battery during the test, there is danger of the battery exploding or of other damage to the battery or the testing apparatus.
There have been certain attempts to overcome these hazards, but such attempts have not provided an adequate solution. One such previous attempt is characterized by providing a limitation upon the time period within which the test was conducted. Such a testing device is disclosed in U.S. Pat. No. 2,632,793 to Linn which discloses a testing device having a timer controlled switch in the load circuit. While providing some control over the time period of the test, the device of the Linn patent does not provide any protection to the battery or the testing device against abnormally high current. Further, the time period of the test is entirely preset with the device of the Linn patent and there is no provision for variance of the time period which is desirable in some instances to accommodate particular conditions encountered during a test.
Another such previous attempt is characterized by providing protection to the testing device against abnormally high current, but as far as is known, such attempt provided neither protection to the battery nor any control over the duration of the test. An example of such a testing device is disclosed in U.S. Pat. No. 2,229,009 to Berry.